This invention relates to control of the RF emissions generated by Magnetron tubes or solid state devices as generally deployed in microwave ovens and electrode-less sulfur lighting structures both operating primarily in the 2.4 to 2.5 GHz ISM band.
Magnetron tubes by way of their intended operation are a primary source of incoherent RF noise. Used in lighting structures and worldwide in over more than 200 million microwave ovens, magnetrons generate a great deal of RF noise in the 2.4 to 2.5 GHz ISM band. They are by far the greatest and most significant source of noise in this band.
The RF noise generated presents a problem for wireless communication systems that also occupy the 2.4 to 2.5 GHz ISM Band. Wireless communication devices use this ISM band particularly because the band is unlicensed and available internationally. Although magnetrons can and do operate in other bands, for the purpose of describing the present invention, references will only be made to the RF noise generated by magnetrons as is present in the 2.4 to 2.5 GHz ISM band. It will be understood that the same principles can be used regardless of the band of operation.
Radio frequency (RF) transmissions in the 2.4 to 2.5 GHz ISM Band have historically had to deal with the presence of man-made noise from microwave ovens. The noise emanates from the oven by leakage through the enclosure of the oven. The leakage noise is periodic and has a radiated output power approximately 20 dB greater in strength than that allowed by the FCC for operation of Part 15 non spread spectrum radios. Most recently, lighting structures are being introduced that incorporate multiple magnetrons operating continuously on all three phases of the AC power grid. The application of these lighting structures present significant interference to wireless communication links at separations of nearly a half mile.
There are several well known ways to perform wireless communication in the presence of an operating magnetron and one of those ways is to use spread spectrum techniques. One type of spread spectrum technique used by wireless communication links is called direct sequence. Direct sequence spreads the communication signal over a band which is much larger than the bandwidth of the information signal so that the narrow band noise from the noise source has a reduced effect on the demodulated signal to noise ratio. This technique however is relatively expensive to implement, and does not work well if the receiver is located very close to the noise source. Another way to communicate in the presence in the presence of magnetron noise as found in microwave ovens is described in U.S. Pat. No. 5,574,979, issued Nov. 12, 1996 to West, entitled xe2x80x9cPeriodic Interference Avoidance in a Wireless Radio Frequency Communication Systemxe2x80x9d. This patent demonstrates a potential solution by avoiding microwave oven periodic noise by sensing the periodicity of the AC power line main in which the oven is connected to. Unfortunately this technique does not work for periodic noise sources other than microwave ovens or in cases where multiple magnetron noise sources exist operating on different AC phases. When the microwave sources operate on different AC phases, there are no gaps left to communicate in using the technique disclosed by West.
Therefore an improvement is needed when the presence of multiple magnetrons operating simultaneously on different phases exist in the same environment and frequency band with wireless communication devices.
This need is met according to the present invention by providing a wireless control system for use in a system having a plurality of periodic noise sources. The control system includes an antenna; an RF receiver connected to the antenna for receiving RF noise from an external periodic noise source; a phase synchronization circuit connected to the RF receiver for generating a clock signal that is in phase with the external periodic noise; and a noise source control circuit connected to the phase synchronization circuit for receiving the clock signal and controlling a periodic noise source, whereby the periodic noise sources in the system are synchronized to emit their periodic noise in phase with each other.
The present invention has the advantage that RF communication can occur during the quiescent periods of the synchronized periodic noise.